The present invention relates to a resin molding type optical module having an optical device and an optical fiber packaged with a resin, an optical fiber communication apparatus using the resin molding type optical module, and an optical communication system.
Recently, great demands for lowering the cost of the optical module have been made in order to introduce the optical fiber communication system into the subscriber network system on a full scale. From a viewpoint of this, with respect to the packaging technology, a resin sealing method (a plastic package method) is influential in place of a hermetic sealing method for a metallized package or a ceramic package which has heretofore occupied the mainstream in the field of optical devices. This is because the resin sealing method is suitable for mass- and inexpensive production.
In the past, in the field of general semiconductor devices such as LSI and hybrid IC, the following various methods have been known as resin sealing methods. (1) a transfer molding method (a method for compressing preheated powdery resin to transfer it to a mold), (2) a casting injection method (method for injecting a liquid resin into a mold frame), (3) a potting injection method (a method for injecting a liquid resin into a resin case), (4) a cap sealing method (a method for adhering a cap to a hollow case with resin), (5) a dipping method (a method for dipping an element into a resin liquid vessel), and (6) a dropping method (a method for dropping a liquid resin onto an element).
Further, the following examples in which the aforementioned resin sealing methods are applied to the optical module have been known. For example, there are Japanese Patent Application Laid-Open No. 2-271308 (Article 1), Japanese Patent Application Laid-Open No. 1-304405 (Article 2), Japanese Patent Application Laid-Open No. 7-321407 (Article 3), Proceedings of the Conference of the Institute of Electronics, Information and Communication Engineers in 1996, Separate Volumexe2x80x94Electronics 1, pages 478 to 479 (Article 4), the same collection, page 216 (Article 5), and the same collection, page 207 (Article 6).
Article 1: In the receptacle type optical module for fiber optic transmission, a hermetic seal by way of a metallized package and a resin seal by way of transfer molding are jointly used. A laser diode and a photodiode are once hermetically sealed in a can type metallized package, and the can type metallized package is molded by the transfer molding method together with electronic circuit parts and a lead frame.
Article 2: In the receptacle type module, a potting injection type method is used. A resin case comprises a black epoxy resin molded article. A cylindrical receptacle is provided in part thereof. A light emitting diode and a light receiving diode are installed on a lead frame, and are received in the resin case. The resin case are filled with transparent epoxy resins by potting. The light emitting diode or the light receiving diode is directly sealed by the transparent resin.
Article 3: This is concerned with a pickup light source of an optical disk. In this example, a casting injection method (or a transfer molding method) and a resin sealing method by way of a dropping method are jointly used. The laser diode is fixedly secured to the lead frame through a heat sink, and these are sealed by casting of transparent epoxy resins. A silicone resin is coated on the surface of the laser diode by the dropping method in order to prevent the optical damage of the sealed resin caused by emitting light of laser and the peeling of an interface between the laser diode and the sealed resin.
Article 4: In the pigtail type module for fiber optic transmission, a casting injection method is employed. In this example, the laser diode and the bare portion of the pigtail fiber are sealed with resin. That is, the laser diode and the extreme end of the bare fiber are secured to the heat sink, and the heat sink is fixedly secured to the metallic stem. They are molded by casting of transparent epoxy resins. The jacket portion of the pigtail fiber is not sealed with resin.
Article 5: In the pigtail type module, a hollow resin case is closed by a cap sealing method. The laser diode and the bare portion of the pigtail fibers are secured to a silicon base plate, and the base plate and the jacket portion are secured to the resin case. A lead frame is insert-molded in the resin case. The bare fiber and the base plate, the jacket and the resin case, and the cap and the resin case are bonded one another by ultraviolet setting resins.
Article 6: In the receptacle type module, the cap sealing method and the transfer molding method are jointly used. A laser diode, the extreme end of a ferrule with fiber, and a lead frame are secured to a silicon substrate to constitute a substrate assembly. The laser diode and the ferrule are once sealed by adhering a silicon cap on the substrate with the epoxy resin, and the substrate assembly is sealed by the transfer molding of black epoxy resins except the rear end of the ferrule and the outer lead portion of the lead frame. The receptacle is constituted by a part of the transfer molded article, the rear end of the ferrule and a housing provided by other parts.
The plastic package is influential for lowering the cost of the optical module as compared with the metallized package or the ceramic package, but has difficulties such that generally, the moisture permeability is high, and the coefficient of thermal expansion is large. These factors synthetically lower the reliability of the plastic package. It is therefore important, for putting the plastic module in practical use, how to secure the reliability while making use of the merit of lowering the cost of the plastic package.
It is concretely necessary to make consideration relative to the aforementioned problems from the following two aspects. First, the moisture resistance should be increased in respect of constituent parts of the module such as an optical device, an optical fiber, a base plate and so on. Secondly, with respect to the optical coupling between the optical device and the optical fiber, it is necessary to suppress extremely highly a deviation in position caused by the thermal stress, the external force, the molding pressure, etc. In particular, in the semiconductor laser module, a demand relative to such a position is severe. This is because the spot size of the laser diode is smaller than the spot size of the light emitting diode and the light receiving diameter of the photodiode.
Any of the aforementioned prior arts have both merits and demerits with respect to such demands as noted above, and fail to respond to the demands of the current industrial world. The present invention is a new invention in connection with these various matters. The aforementioned problems with respect to the prior arts will be briefly mentioned in order to better understand the background of the present invention.
Article 1: The number of parts and the number of assembly steps so increase as not to make a good use of the plastic package, i.e., the low cost. That is why the metallized package and the plastic package are jointly used.
Article 2: The cylindrical receptacle is formed in a part of the resin case. Considering the dimensional accuracy of the receptacle itself and the deformation of the receptacle caused by the insert- and pull force of connector and the thermal expansion, the module in Article 2 can be applied to a light emitting diode having a large spot size but is not suitable for a laser diode having a small spot size.
Article 3: A light source for an optical disk is concerned, which is not used for transmission of an optical fiber as in the present invention. Naturally, consideration of the seal of fiber and the reliance of optical coupling is not taken in Article 3.
Article 4: Only the bare portion of the pigtail fiber is sealed with resin, and the jacket portion is exposed to outside. Accordingly, the thermal stress and the external force are concentrated on the interface between the bare fiber portion and the jacket portion to bring forth a problem in that the bare fiber is broken. There is a difficulty that since when the casting is performed, voids tend to be mixed, water moves in from the channel to corrode optical ends of optical devices and electrodes.
Article 5: While the pigtail fiber is received in the hollow resin case, reference is not made to the thermal stress and moisture resistance of the resin case. Further, reference is not made to materials for the resin case and molding method. In this technique, various problems occurs unless various items mentioned above are sufficiently selected. That is, due to a difference in the coefficient of thermal expansion between the bare fiber (quartz glass) and the resin case, the bare fiber protrudes from the jacket, and the crack occurs in the bare fiber due to the concentration of stress. Further, vapor permeated into the hollow case becomes dewed on the surface of the optical device or the bare fiber to give rise to the corrosion of the optical device, or to progress the growth of crack, resulting in the rupture of the bare fiber.
Article 6: The optical device and the ferrule with fiber are sandwiched between the silicon substrate and the silicone cap, and sealed. However, the elastic modulus of the resin package member and the anisotropy of the thermal coefficient of expansion of the resin package member are not taken into consideration.
As briefly mentioned above, the prior arts lack some consideration in relation to the number of parts, thermal stress and moisture resistance concerned with the cost. The present invention provides an optical module compatible with the lower cost and the higher reliance by the plastic packaging technique.
A first object of the present invention is to secure the reliability of an optical module while reducing the molding cost of a resin case type package.
A second object of the present invention is to secure the long-term stability of an optical coupling between an optical element and an optical fiber while reducing the molding cost of a resin case type package. That is, it is to provide a means which suppresses deformation of the resin case caused by the change in temperature and the external force to reduce stress applied to constituent members of the optical module.
A third object of the present invention is to provide a means for further enhancing the moisture resistance of constituent members of an optical module such as an optical device and an optical fiber while reducing the molding cost of a resin case type package. Thereby, the long-term stability of the optical module is to be secured. By the joint use with the means for securing the long-term stability of the optical coupling between the optical device and the optical fiber mentioned in the above second object, it is possible to secure more sufficient and long-term stability of the optical module.
A fourth object of the present invention is to secure the reliability of an optical module while reducing the molding cost of a comprehensive molding type package.
A fifth object of the present invention is to secure the long-term stability of an optical coupling between an optical device and an optical fiber while reducing the molding cost of a comprehensive molding type package. That is, it is to provide a means which suppresses deformation of the resin case caused by the change in temperature and the external force to reduce stress applied to constituent members of the optical module.
A sixth object of the present invention is to provide a means for further enhancing the moisture resistance of constituent members of an optical module such as an optical device and an optical fiber while reducing the molding cost of a comprehensive molding type package. Thereby, the long-term stability of the optical module is to be secured. By the joint use with the means for securing the long-term stability of the optical coupling between the optical device and the optical fiber mentioned in the above fifth object, it is possible to secure more sufficient and long-term stability of the optical module.
A seventh object of the present invention is to provide a means for constituting the optimal electric connection to an optical device while securing the reliability of an optical module and the reduction of the molding cost of a resin case type package.
An eighth object of the present invention is to provide a means for constituting the optimal electric connection to an optical device while securing the reliability of an optical module and the reduction of the molding cost of a comprehensive molding type package.
A ninth object of the present invention is to provide an optical communication apparatus having an optical module of low cost and high reliability mounted thereon, and an optical communication system.
Various inventions disclosed in the present specification particularly relate to the following two aspects in solving the aforementioned problems. The first is an aspect of a resin package molding method. The second is an aspect of a method for mounting an optical device and an optical fiber into the resin package. In the present specification, the resin package molding method is divided roughly, and the individual molding methods will be explained in detail.
The resin package molding method is divided roughly into two kinds. First, a method of using a resin case premolded (hereinafter referred to as a resin case type) is used. Secondly, a method for comprehensively insert-molding an optical device with other various constituent parts (hereinafter referred to as a comprehensive molding type method) is used. In the case of the above-described resin case type, an injection method is suitable for molding a resin case. On the other hand, in the comprehensive molding method, a transfer molding is suitable.
It is noted that the optical devices in the present specification include active optical devices such as a semiconductor laser device, an optical amplifier, an optical modulator, an optical switch, etc., passive optical elements such as a semiconductor light receiving device, an optical coupler, an optical wavelength multiplexer/demultiplexer, etc., a hybrid optical integrated circuit in which optical elements are mounted on an optical waveguide base plate or an electronic circuit base plate, a monolithic integrated optical circuit having optical elements and an electronic circuit integrated, and an optical element as fiber. Further, as the aforementioned various optical devices, a semiconductor device having an active region mainly formed of a semiconductor material, and a dielectric optical device having an active region formed of a dielectric material can be also used.
As optical fibers, there can be used, in addition to a single mode quartz fiber, a multimode fiber, a plastic fiber, and so on. Not only one but a plurality of optical fibers can be used. Forms of fibers include a form used as a fiber array and a fiber ribbon, and a form for removing or connecting fibers on some surfaces of the package.
In the following, with respect to the details of the present invention, a method of a resin case type will be first explained, and a comprehensive molding method will then be explained.
 less than Resin Case Type Molding Method greater than 
Main forms of the present invention belonging to the resin case type are as listed below. It is noted that the contents of detailed explanation thereof, further improved inventions, and modified inventions will be also explained.
A first mode of the optical module according to the present invention has the following constitution. That is, there comprises an optical device, an optical fiber optically coupled to the optical device, and a resin case member for mounting at least the optical device and the optical fiber thereon, the direction along an optical axis of the optical fiber; being the direction of the high elastic modulus of a resin material of a main portion along the optical axis of the optical fiber of the resin case member.
Since the direction of the optical fiber is the direction of the high elastic modulus in the resin having the anisotropy in the elastic modulus particularly at the main portion along at least the optical axis of the optical fiber in the base of the resin case member, the deformation of the resin case due to the mechanical external force and the difference in the thermal expansion is suppressed. The resin case member is inexpensive as compared with the ceramic package, and the resin case is free from deformation whereby the manufacturing yield can be enhanced, and the manufacturing cost price can be reduced.
A second mode of the optical module according to the present invention comprises an optical device, an optical fiber optically coupled to the optical device, and a resin case member for mounting at least the optical device and the optical fiber thereon, the direction along an optical axis of the optical fiber being the direction of the low coefficient of thermal expansion in a resin material of a main portion at least along the optical axis of the optical fiber in the resin case member.
Since the direction along an optical axis of the optical fiber is the direction of the low coefficient of thermal expansion in a resin material at a main portion along the optical axis of the optical fiber in the resin case member, the deformation of the base due to the heat is small, and the misalignment for coupling between the optical device and the optical fiber does not occur. It is noted that the generation source of heat for occurrence of such a phenomenon as described in question is for example, a change in temperature of external environment or heat generation of the optical device itself in the package.
The resin case member is inexpensive as compared with the ceramic package, and the resin case is free from deformation whereby the manufacturing yield can be enhanced, and the manufacturing cost price can be reduced.
A third mode of the optical module according to the present invention comprises an optical device, an optical fiber optically coupled to the optical device, and a resin case member for mounting at least the optical device and the optical fiber thereon, the orientation of a molecular chain of the resin being substantially parallel with the optical axis of the optical fiber in a main portion along an optical axis of the optical fiber in the resin case member.
Since the orientation of a molecular chain of the resin of the main portion along the optical axis of the optical fiber being substantially parallel with the optical axis of the optical fiber, it is possible to enhance the elastic modulus of the case in the direction of orientation of the molecular chain and to reduce the coefficient of thermal expansion as a result. Accordingly, the deformation of the base due to the external stress or thermal stress is small, and the deviation in position between the optical device and the optical fiber does not occur. It is noted that the generation source of heat for occurrence of such a phenomenon as described in question is for example, a change in temperature of external environment or heat generation of the optical device itself in the package.
The resin case member is inexpensive as compared with the ceramic package, and the resin case is free from deformation whereby the manufacturing yield can be enhanced, and the manufacturing cost price can be reduced.
A fourth form of the optical module according to the present invention comprises an optical device, an optical fiber optically coupled to the optical device, and a resin case member for mounting at least the optical device and the optical fiber thereon and having a main flowing direction of the resin substantially parallel with the optical axis of the optical fiber.
According to the above-described molding method, the direction of the optical axis of the optical fiber is generally parallel with the orientation of the molecular chain of the resin constituting the lengthwise direction of the resin case. Therefore, it is possible to enhance the elastic modulus of the case in the direction of orientation of the molecular chain and to reduce the thermal expansion rate as a result.
Preferably, in molding the resin case as described, there is provided a gate for injecting the resin at a fiber supporting portion, a part in the vicinity thereof, or a part opposite to the supporting portion to inject the resin into a mold. By injecting the resin from the aforementioned part, it is possible to make the direction of the optical axis of the optical fiber and the orientation of the molecular chain of the resin constituting the lengthwise direction of the resin case generally parallel. This molding method is suitable to be used for (1) the pigtail type optical module and (2) the receptacle type optical module.
The resin case member according to the aforementioned molding method is inexpensive as compared with the ceramic package, and the resin case is free from deformation whereby the manufacturing yield can be enhanced, and the manufacturing cost price can be reduced.
In this case, more practically, it is preferable that a lead frame is premolded integrally with a resin package member. That is, when the resin is caused to flow substantially parallely with the optical axis of the optical fiber to mold the resin package member, the lead frame is inserted in advance at a predetermined position, and a thermoplastic resin is caused to flow for injection molding.
According to this means, since the resin case and the lead frame as an electric terminal can be integrated and supplied, the handling in assembly of the module is simple. Further, since the optical device and the optical fiber can be firmly located to the substrate, optical coupling can be stabilized without disturbing alignment between the optical device and the fiber by the distortion of the case caused by the external force or the change in temperature. Furthermore, heat generated by the optical device is released through the lead frame.
In the case where the optical module is produced using the resin case type, it is important, from a viewpoint of an idea of the method for molding the resin package, when the resin case is injection-molded, to place the optical fiber in the resin case so that the flowing direction of the thermoplastic resin within the mold is generally parallel with the direction of the optical axis of the optical fiber. When various members are sealed in the case, it is possible to suppress the deformation of the case caused by the external force or the change in temperature, and suppress the deformation of the case caused by the change in temperature or the external pressure. Because of this, it is possible to prevent an occurrence of deterioration in optical coupling characteristics caused by the positional deviation between the optical device and the fiber, and cracks in the fiber surface, as a consequence of which the reliability of the optical module can be enhanced. The optical coupling between the optical device and the fiber can be maintained stable for a long period of time.
There are two kinds of case materials for the resin case type, which are a thermosetting resin and a thermoplastic resin. A typical example of the thermosetting resin that can be mentioned is an epoxy resin. Examples of the thermoplastic resins that can be mentioned include a liquid crystal polymer (LCP) of a glass fiber-reinforced grade, a cross-linked type polyphenylene sulfide (PPS) resin, a linear PPS resin, a polybutylene terephthalate (PBT) resin and so on of a filler-reinforced grade and a carbon fiber-reinforced grade.
As the resin used for the resin case method, the thermoplastic resin is particularly preferable. Because the thermoplastic resin has the advantages as follows: (1) The molding cycle time is short as compared with the thermosetting resin. (2) The resin loss ratio is low. (3) Recycle materials can be used. That is, together with the merit of the above (1), since the using quantity of resins can be reduced, it is useful for reducing the cost. (4) Burr is small due to the low pressure injection molding. (5) The cure after molding is unnecessary. On the basis of these advantages, it is possible to produce the resin case at lower cost. It is noted that the fact that a molding temperature is relatively high poses little problem in production of the resin case.
Further, it is possible to easily arrange the orientation of the molecular chain by carrying out the injection molding with the resin mentioned above. Particularly, it is possible to more easily arrange the orientation of the molecular chain with a linear PPS or a liquid crystal polymer. Accordingly, it is possible to realize lower stress by placing the fiber within the case along the aforementioned orientation to achieve the higher reliability as a result. Since the thermoplastic resin allows the molecular chain to be oriented in the flowing direction of resin when molding as described above, it is important to take into mechanical and thermal anisotropy. Deformation tends to occur relative to external force, or time passage positional deviation (creep) between the optical device and the fiber or crack in fiber due to the thermal stress sometimes is induced unless the dependency of elastic modulus or coefficiency of thermal expansion is taken into consideration.
It is noted that the thermosetting resin can be also used for the present method of resin case type. However, the use of the thermoplastic resin is advantageous in terms of price as compared with the use of the thermosetting resin.
Next, the sealing of the optical device and the optical fiber within the resin package in the case of the resin case type will be explained.
In the case of the resin case type, the procedure itself of the manufacturing method may employ the usual procedure. At least the optical device and the optical fiber are placed on the base of the resin package, and the package is completed using the cap. More practically, the substrate having the optical device and the optical fiber secured thereto is placed on the resin case in which the lead frame is inserted except the outer lead portion and subjected to injection molding.
In the resin case type, the sealing method for the optical device and the optical fiber within the package can be mainly classified into three kinds. A first method comprises a method for filling a transparent resin into a resin case by a potting injection method, a second method comprises a method for mounting a cap on a resin case to seal the interior of the case leaving to be hollow, and a third method comprises a method for sealing a resin case and a cap after a transparent resin has been dropped onto an optical device and a fiber. Of these methods, the first method, i.e., the potting injection method is more preferable.
The second method has a problem of the dewing to the optical device and the fiber, and the deterioration of the optical device and the rupture of the fiber resulting therefrom. As compared with the first and third methods, the first method, i.e., the potting injection method in which the case is internally filled with resin is more preferable in order to suppress the deformation of the resin case and the stress of the fiber as less as possible. In this case, the optical device and the optical fiber are coated directly with the transparent resin.
According to this means, the optical device and the optical fiber are coated directly with the transparent resin whereby water moved into the resin case (which cannot be avoided under the high temperature and high humidity environment for a long period of time) can be prevented from moistening to the optical surface of the optical device and the surfaces of the electrode and the fiber.
Further, the joint use of the sealing method for the optical device and the optical fiber within the package and the molding method for various resin package members according to the present inventions can obtain the following effects. That is, together with the effect of the lower stress based on the molding method for the resin package member, the adhesion of the transparent resin to the optical device and the optical fiber can be secured. The stress of the optical device itself is relieved because the resin case has the high elasticity and lower thermal expansion, and the adhesion of the transparent resin to the optical element and the optical fiber and the transparent resin can be secured. Accordingly, there is the effect that the corrosion of the optical device and the crack of the fiber caused by formation of a water film can be prevented, and the moisture resistance can be enhanced.
Further, the change in temperature of the external environment is relieved within the resin case. Furthermore, the enhancement of the environment resistance by the transparent resin used to seal the optical fiber is remarkable.
The transparent resins for directly coating the optical device and the fiber that can be used include thermosetting resins, for example, such as a silicone gel of a silicone resin, silicone rubber, a low stress epoxy resin, an acrylic resin, a urethane resin, etc.
It is noted that the laser diode for the optical disk mentioned in Article 3 in the column of the prior art is coated directly with the silicone resin as measures for optical damage. However, since the laser diode for fiber optic transmission has long in oscillation wavelength and emits relatively smaller optical output, the optical damage caused by absorption of light and thermal decomposition as in the optical disk is hard to occur. Accordingly, in the optical transmission system, it is less necessary to expect for the packaging resin the role as measures for optical damage as in Article 3. Article 3 is different from the present invention in a viewpoint of such a selection.
 less than Comprehensive Molding Method greater than 
In the following, the comprehensive molding method will be explained.
The optical module in the fifth mode of the present invention according to the comprehensive molding method has the following constitution. That is, when the optical device and the optical fiber are inserted for transfer molding, the thermosetting resin is flown so as to be generally parallel with the direction of the optical axis of the optical fiber within the mold for molding. This method can reduce the flew resistance of the resin applied the fiber, and reduce the positional deviation and the residual distortion of the fiber. Accordingly, it is possible to prevent the deterioration of the optical coupling characteristic caused by the positional deviation between the optical device and the fiber and the occurrence of the crack in the fiber surface, thus enabling enhancement of the reliability of the optical module as a result.
Further, the present means has the effect that the optical device and the optical fiber can be molded stably and comprehensively in a short period of time by the transfer molding, and the cost can be reduced. Further, the molten thermosetting resin is flown along the fiber placed within the mold whereby fluctuation of the optical coupling characteristic during molding can be suppressed (for example, the low viscosity resin and the low speed molding are further effective), and the residual stress applied to the fiber after molding can be reduced. For example, the low elastic resin and the low thermal expansion resin are further effective. With this, the reliability of the optical module including the moisture resistance can be enhanced.
It is noted that when in molding, for example, the use of the low viscosity resin and the low speed molding are further effective in order to display the effects of the present invention. For solving the problem after molding, the use of, for example, the low elastic resin and the low thermal expansion resin is further effective.
As the resin used for the comprehensive molding method, the thermosetting resin is preferable. The typical examples of the base resin that can be listed include an epoxy resin and a silicone resin. Of course, a filler and a elasticizer as desired can be added similar to the case of the practical use of the usual thermosetting resin.
The comprehensive molding generally includes two methods, which are a casting injection method and a transfer molding method. For the former, mainly a liquid epoxy resin is used, and for the latter, mainly a tablet is used in which a powdery epoxy resin is pressed.
The transfer molding method is suitable for the lower cost and mass production. Because the transfer molding method has the following advantages as compared with the casting injection method. That is, (1) the molding time is short, (2) the vacuum defoaming process is unnecessary, and (3) the shape dimension and reliability are stable.
However, in the transfer molding in the case where there are no metallized package and cap, the transfer pressure of resin is applied to the optical device and the fiber, resulting in the positional deviation between the optical device and the fiber, and the distortion of the fiber and the optical device-mounted base plate. Accordingly, it is necessary to take the flowing direction of resin during molding into consideration. This positional deviation deteriorates the coupling characteristic of the optical device and the fiber. Further, since the distortion acts as the internal residual stress, this influences on the long-term reliability of the optical module.
It is noted that even in the resin case type, the orientation of the molecular chain by the flowing direction comprises a main point, and it is understood that the flowing direction is important for both the resin case type and the comprehensive molding type.
In this case, in the case of the transfer molding, it is suitable that the lead frame is inserted in advance into a predetermined position, and the thermosetting resin is flown generally parallel with the optical axis of the optical fiber to effect the transfer molding.
According to this means, the optical device and the optical fiber can be stable held on the base plate, and in addition, the base plate is fixed upwardly or downwardly of the lead frame and the transfer molding is performed to enable electric connection simply.
The sealing method for the optical device and the fiber in the comprehensive molding type can be mainly classified into four methods as follows: A first method is a method for directly molding an optical device or an optical fiber with a transparent resin, a second method is a method for molding an optical device or a fiber with an opaque resin (colored, mainly black) after being sealed with a cap, a third method is a method for molding them using a transparent resin after dropping a transparent resin on them, and a fourth method is a method for further molding them using a opaque resin after dropping it.
Since a cap is preferably omitted in order to reduce the number of parts to lower the cost, it is necessary for the resin for directly coating the optical device to be transparent. In order to prevent the stray light which comes in and goes out of the module, it""s outermost surface is preferably opaque. Accordingly, the fourth method which has not been present in the past is more desirable, which molds an opaque resin on a dropped transparent resin.
In the case of the comprehensive molding method, the following step is taken. At least the optical device and the optical fiber are placed on the base of the package, and the transparent resin is dropped on the optical device and the fiber to fix them. By doing so, the optical device and the fiber are directly encapssulated with the transparent resin, after which the transfer molding is performed.
More practically, at least the optical device, the fiber, and the lead frame are fixed to the substrate, and the base plate assembly is inserted to the module, and the transfer molding is performed except the outer portion of the fiber and the outer lead portion of the lead frame.
According to the means for directly coating the optical device and the optical fiber with the transparent resin, the deterioration of the optical device or the fiber caused by the moisture absorption of the transfer molding package can be prevented, and in addition, the molding pressure applied to the coupling portion between the optical device and the optical fiber can be dispersed, and the residual stress after molding can be relieved. Accordingly, there is the effect that the optical coupling characteristic between the optical device and the optical fiber can be further stabilized, and the reliability of the optical module can be further enhanced.
In the module for fiber optic transmission, the silicone resin is not necessary for preventing optical damage. However, silicone is advantageous in the following point. Paying attention to the fact that the elastic modulus of the silicone resin is lower than that of the epoxy resin, the thermal stress applied to the optical device or the fiber is relieved so that the interface between the optical device and the resin is prevented from peeling. Accordingly, the corrosion caused by formation of a water film at the interface can be prevented.
It is noted that in the case where the transfer molding is employed in the comprehensive molding type, since the transfer pressure is applied to the transparent resin, the elastic modulus of the transparent resin should be high to some extent in order to prevent deformation. That is, it is necessary to select a transparent resin having the elastic modulus compatible with the lower thermal stress and the deformation prevention.
Various optical modules described above are mounted on the wiring substrate of the optical communication apparatus to make the optical communication apparatus high reliability and realize it at less cost. In this way, it is possible to provide an optical communication system which has high reliability and is inexpensive.
The effects of the present invention can be arranged as follows:
According to the first mode of the present invention, since the direction of the optical axis of the optical fiber of the resin case member is the direction of high elastic modulus in the resin, particularly at the main portion along at least the optical axis of the optical fiber in the base, the deformation of the base caused by the external heat is small, and the positional deviation between the optical device and the optical fiber does not occur.
According to the second form of the present invention, since the direction along an optical axis of the optical fiber is the direction of the low coefficient of thermal expansion in a resin material at a main portion along the optical axis of the optical fiber in the resin case member, the deformation of the base caused by the external heat is small, and the positional deviation between the optical device and the optical fiber does not occur.
According to the third mode of the present invention, since at the main portion supporting at least the optical axis of the optical fiber in the resin case, the orientation of the molecular chain of the resin is substantially parallel with the optical axis of the optical fiber, the elastic modulus of the case in the direction of orientation of the molecular chain is enhanced, and as a result the thermal expansion rate can be reduced. Accordingly, the deformation of the base caused by the external heat is small, and the positional deviation between the optical device and the optical fiber does not occur.
According to the fourth mode of the present invention, the direction of the optical axis of the optical fiber is generally parallel with the orientation of the molecular chain of the resin constituting the lengthwise direction of the resin case. Because of this, the elastic modulus of the case in the direction of the orientation of the molecular chain is enhanced, and as a result, the thermal expansion are can be reduced. Accordingly, the deformation of the case caused by the change in temperature and the external force can be suppressed, and the stress applied to the constituent member of the optical module is reduced. As a result, the optical coupling between the optical device and the fiber can be maintained stable for a long period of time.
According to the fifth form of the present invention, it is possible to comprehensively mold the optical device and the fiber by the transfer molding stably and in a short period of time, the lower cost can be achieved, the molten thermosetting resin is flown along the fiber installed within the mold to enable the suppression of variation of the optical coupling characteristic during molding, and the residual stress applied to the fiber after molding can be relieved. Accordingly, the reliability of the optical module including the moisture resistance can be enhanced.
The present invention is capable of providing an optical communication apparatus and an optical communication system which are low in price and has a high reliability.